In an optical communication system or optical data communication system, an optical module incorporating optical elements such as laser diodes is used. This optical module is now installed in homes along with recent progress made in computer hardware and communication networks. Thereby, demand for small-sized, highly integrated and low-cost optical modules arises.
To meet such demand, the development of the following optical module is under way. The optical module comprises a substrate on which optical elements such as light emitting elements and light-receiving elements and a conductor pattern are formed in a package and is connected to optical fibers or optical waveguide component for communication.
The substrate constituting the optical module is preferably a silicon substrate. The reason for this is that silicon (Si) has excellent workability. Therefore, for example, the silicon substrate has such an advantage that it is easy to put alignment marks for position determination on the silicon substrate when optical elements are to be mounted or to form V-shaped grooves for the position determination of optical fibers in the silicon substrate when the optical fibers are to be arranged.
Further, silicon has excellent heat radiation properties. Therefore, the silicon substrate has such an advantage that it can serve as a heat sink for radiating heat from optical elements. The silicon substrate has a further advantage that a raw material for the manufacture of the silicon substrate can be acquired at a low cost and has stable quality.
The silicon substrate having the advantages, on which optical elements, a conductor pattern and optionally the alignment marks and V-shaped grooves are formed is called “silicon platform for optical modules.”
FIG. 5 shows a typical example of the silicon platform for optical modules. The silicon platform for optical modules shown in FIG. 5 has a silicon substrate 505 and an SiO2 insulating layer 507 which is an oxide layer formed on the silicon substrate 505. A light-receiving element 501 and a light emitting element 504 all of which are optical elements are mounted on the SiO2 insulating layer 507 through a conductor pattern 506. A microstrip line structure is formed on the SiO2 insulating layer 507 at a position other than the area for mounting the optical elements 501 and 504. This microstrip line structure is a laminate consisting of a ground film 510, a dielectric film 509 and signal lines (conductor pattern) 508, all formed in the order named.
The conductor pattern 506 formed in the area for mounting the optical elements 501 and 504 and the signal lines 508 of the microstrip line structure are electrically connected to each other by lead wires 502. Thereby, the optical elements 501 and 504 are electrically connected to the signal lines 508 by the conductor pattern 506 and the lead wires 502.
The silicon substrate 505 has a thickness of about 1 mm, for example. The dielectric film 509 is made from polyimide, for example. This dielectric film 509 has the function of insulating the ground film 510 from the conductor pattern 508.
The silicon platform for optical modules shown in FIG. 5 is constituted as described above. A typical example of optical module comprising this silicon platform for optical modules is shown in FIG. 6. In FIG. 6, the silicon platform for optical modules is mounted on a substrate 601. A wiring pattern 602 and lead frames 611 are formed and a part 603 such as a preamplifier IC are mounted on the substrate 601. External connection terminals are further provided on the substrate 601 as required.
The substrate 601 having the silicon platform for optical modules and the part 603 mounted thereon, for example, is incorporated in a package (not shown) together with an optical ferrule 613 shown in FIG. 6 to constitute an optical module. The optical ferrule 613 is connected to one ends of optical fibers 612. The other ends of the optical fibers 612 are drawn out to the outside of the package. To store the optical ferrule 613 in the package of the optical module, the optical ferrule 613 is arranged such that the optical fibers 612 can be optically connected to the optical elements 501 and 504.
Since the silicon platform for optical modules shown in FIG. 5 has both the light-receiving element 501 and the light emitting element 504 as described above, the optical module shown in FIG. 6 comprising the silicon platform for optical modules can be an optical module for two-way communication.
Both the light-receiving element 501 and the light emitting element 504 are mounted on the silicon platform for optical modules shown in FIG. 5 and FIG. 6 as described above. As a matter of course, there are the following silicon platforms for optical modules besides the silicon platform. For example, there is a silicon platform for optical modules, which comprises only one of the light-receiving element 501 and the light emitting element 504. As shown in FIG. 7, there is also a silicon platform for optical modules which comprises an optical array element 701, on which a plurality of light-receiving elements 501 or light emitting elements 504 are disposed in an array.